Conventionally, cylindrical thermoelectric modules to perform power generation by utilizing exhaust heat of exhaust pipes of automobiles, boilers and the like to recover energy are known. For example, the one disclosed in Japanese Patent Laid-open No. 61-254082 is called a first prior art. FIG. 36 shows a thermoelectric module disclosed in the same Laid-open Patent, and the first prior art will be explained below based on FIG. 36. In FIG. 36, a thermoelectric module 110 includes a hollow pipe 112 being an inner cylinder and a housing 111 being an external cylinder. P-type and n-type thermoelectric elements 113 and 114 are alternately placed in a circumferential direction between the pipe 112 and the housing 111.
First end portions of the thermoelectric elements 113 and 114 are connected by an inner electrode 116, and the inner electrode 116 is in contact with a pipe 112 via an insulator (not shown). The other end portions of the thermoelectric elements 113 and 114 are connected by an outer electrode 115 and the outer electrode 115 is in contact with a housing 111 via an insulator (not shown). For example, when an exhaust gas having heat passes through an inside of the pipe 112, an electromotive force occurs by a Seebeck effect to the thermoelectric elements 113 and 114. This electromotive force is taken from electric power line 129, whereby power generation utilizing exhaust heat is performed.
An example of forming the cylindrical thermoelectric module 110 by using the ring-shaped thermoelectric elements 113 and 114 is described in “Analysis on Power Generating Characteristics of Cylindrical Shaped Thermoelectric Module”, that is the data of New Energy and Environment Study Group, issued by The Institute of Electrical Engineer of Japan on May 15, 2000. This is called a second prior art. A perspective view of the second prior art will be shown in FIG. 37. As shown in FIG. 37, in the second prior art, the ring-shaped thermoelectric elements 113 and 114 are alternately arranged between the pipe 112 and the housing 111, and the disc-shaped electrodes 115 and 116 are placed between them. By a power line (not shown), an electromotive force is taken.
However, the aforementioned prior arts have the problems that will be described as follows. Namely, in the first prior art, as shown in FIG. 36, the electrodes 115 and 116 are constituted to have curvatures along wall surfaces of the cylinders, and the thermoelectric elements 113 and 114 are joined to curved surfaces of the electrodes 115 and 116. In order to realize this, it is necessary to construct the thermoelectric elements 113 and 114 to have curvatures similarly to the electrodes 115 and 116. Otherwise, adhesion between the thermoelectric elements 113 and 114 and the electrodes 115 and 116 is decreased to cause electric resistance, and a current does not flow favorably, thus reducing power generation performance of the thermoelectric module 110.
However, the thermoelectric elements 113 and 114 arc generally produced by cutting sintered wafer and rod materials. Therefore, it is easy to produce them in a columnar shape and a rectangular parallelepiped shape, but it is very difficult to produce the surfaces in contact with the electrodes 115 and 116 to have the curvatures corresponding to the electrodes 115 and 116, as in FIG. 36. Namely, in order to realize such a thermoelectric module 110, it is necessary to produce the thermoelectric elements 113 and 114 in special shapes corresponding to the shapes of the pipe 112 and the housing 111, thus causing the problem of requiring very high cost.
Further, according to the first prior art, the thermoelectric elements 113 and 114, and the electrodes 115 and 116 are joined by soldering. Since the temperature of an exhaust gas sometimes becomes extremely high, the temperature difference between the inner electrode 116 and the outer electrode 115 becomes large. As a result, the pipe 112 expands, and large stress is exerted on the thermoelectric elements 113 and 114 and joint portions, and any one of them is sometimes broken. As an art of preventing breakage of soldering as described above, there is the one disclosed in, for example, Japanese Patent Laid-open No. 3-91272. This is what is made by stacking the p-type thermoelectric element, the electrode at the heat absorption side, the n-type thermoelectric element, and the electrode at the heat exhaust side alternately in one row in this order. By fastening them together, joint portions are eliminated so that even stress caused by heat is exerted thereon, the thermoelectric module is not broken.
However, in the art disclosed in Japanese Patent Laid-open No. 3-91272, a concrete constitution as to how heat is exchanged, for example, when the heat source is solid, or liquid, is not disclosed. The constitution as to how such a thermoelectric module is used, for example, when heat is taken from the exhaust heat of the cylindrical exhaust pipe as in the first and the second prior arts is not described. In the second prior art, the ring-shaped thermoelectric elements 113 and 114 are produced. Such ring-shaped thermoelectric elements 113 and 114 need to be produced by a special order, which requires very high cost.